Aromatic acids from petroleum fractions



United States Patent 3,150,172 ARQMATIC ACllJ S FRQM PETRQLEUItlFRACTKGNS Qarl Serres, in, Hammond, End, and Ellis it. Fields,

Chicago, lllL, assignors to Standard till Company,

(Jhicago, ill, a corporation of Indiana No Drawing. Filed Apr. 17, 1959,er. No. 807,036

9 Claims. (Cl. Edd-52 i) This invention relates to the preparation ofnaphthalene carboxylic acids from readily available petroleum refinerystocks. More particularly, the invention relates to an improved processfor preparing naphthalene carboxylic acids from selected fractions ofcatalytic reformates.

Recently, a large number of carboxylic acid derivatives of naphthalenehave become of interest in the manufac ture of outstanding alkyd resinsand, in ester form, as superior plasticizers. Also, certain of thesenaphthalene carboxylic acids are capable of forming super-polyesterswhich may be cold-drawn into high tensile strength fibers and films.Unfortunately, despite their superiority in certain respects tomononuclear aromatic acids such as phthalic and terephthalic acids, thenaphthalene carboxylic acids are thus far of restricted commercialpracticability by reason of their limited availability. Furthermore,naphthalene carboxylic acids are generally prepared by oxidation of thecorresponding alkyl naphthalene, and there are two monomethylnaphthalenes, two monoethyl naphthalenes, ten dimethyl naphthalenes, andtremendous numbers of higher allcyl naphthalenes, many of which havealmost identical boiling points. Thus the problem of resolving eitherisomeric allryl naphthalenes or isomeric naphthalene carboxylic acids toproduce the pure naphthalene carboxylic acids necessary for suchpurposes as fiber-forming polyesters has raised an almost insurmountabletechnical barrier to their widespread adoption.

It has now been discovered, in accordance with the invention, thatcertain readily-available petroleum refinery streams may be separated bysimple fractional distillation to afford selected fractions whichpredominate in only a small numberor even only onealkyl naphthalene.These selected fractions may then be catalytically oxidized in theliquid phase to produce exceptional yields of relatively purenaphthalene carboxylic acids. Specifically, it has now been discoveredthat the bottoms fraction obtained by removing gasoline-boiling-rangecomponents from a catalytically reformed naphtha, or catalyticreformate, contains only a limited number of isomeric alkylnaphthalenes, and may be resolved into selected fractions or cuts whichwill yield a relatively pure naphthalene carboxylic acid upon oxidationin the oxidation process set forth hereinafter. Gxidation of theselected catalytic rcformate bottoms fraction according to the inventiveprocess is conducted by reacting that fraction with a molecularoxygen-containing gas in the liquid phase in the presence of a catalystcomprising, in conjoint presence, bromine and a heavy metal oxidationcatalyst. By this oxidation, alltyl naphthalenes in the bottoms fractionare converted in high yields to the corresponding naphthalene monoordi-carboxylic acid.

It has further been discovered, however, that extreme care must be takenin preparing the catalytic rcformate bottoms fraction for oxidation.Unidentified materials, presumably hydrocarbons, which are present inreform-ate bottoms fractions which contain components having trueboiling points at 200 mm. absolute pressure of above 405 F. act aspowerful inhibitors to the above liquid phase oxidation process. Even afen percent of these high boiling hydrocarbons are capable of entirelypreventing the conversion of catalytic reformate bottoms fractions intorecoverable naphthalene carboxylic acids.

Patented Sept. 22, 1964 ICC Catalytic reforming, as is well known, is anestablished process for upgrading the octane number of petroleum naphthafractions. The charge naphtha, which may be a virgin distillate, athermal cracked naphtha, a visbreaker naphtha, or blends of suchnaphthas, is processed at elevated temperatures and pressures in thepresence of hydrogen gas over certain catalysts such as platinum-typecatalysts comprising about (Ll-1% platinum on a high surface supportmaterial such as alumina, whereby reactions such as dehydrogenation ofnaphthenes to aromatics, dehydrocyclization of para'lfins to aromatics,and isomerization of normal paraffins to highly branched paraftinsoccur. The products of these reactions all have substantially higheroctane numbers than the naphtha chargin g stock. Such naphtha chargingstocks may have boiling ranges from about 100 to about 400-500 P. for afull boiling range naphtha, but present commercial practice usuallydictates a feed naphtha of about ZOO-400 F. boiling range. Beforesubjecting. the naphtha to catalytic reforming, all or a portion of itmay be pretreated over so-called hydrofining catalysts, e.g. of thecobalt-molybdate type, in admixture with hydrogen gas to saturate anyolefins and decompose organic compounds of sulfur, nitrogen, and oxygento hydrogen sulfide ammonia, and water, respectively, which in excessconcentration are undesirable in the reforming operation.

Conditions for catalytically reforming naphthas to obtain high octanenumber gasoline product and a reformate bottoms fraction for use in theinventive process herein are generally selected to produce the desiredoctane number product, usually an octane number of or above by ASTMresearch method without the addition of tetraethyl lead. The catalyst isdesirably disposed in a plurality of fixed beds of catalyst particles.Reactor inlet temperatures may be between about 880 and about 1000 F.,depending upon other variables to obtain the desired product octanenumber; pressures ranging from about 50 to about 800 pounds per squareinch gage; recycle hydrogen-containing gas rates of from about 1,000 toabout 10,000 standard cubic feet of hydrogen gas per 42-gallon barrel ofnaphtha charge; and liquid hourly space velocities, i.e. pounds ofnaphtha per hour per pound of catalyst, of from about 0.5 to about 5.0may be used. Modern practice currently dictates a reformate octanelevel, research clear, in the -105 octane number class, which requiresreactor inlet temperatures of about 940-980 F., pressures which arepreferably in the range of about 150 to 450 p.s.i.g., recycle ga ratiosof about 3000-6000 s.c.f./b., and liquid hourly space velocities ofabout 1.0- 3.0. Reforming is desirably conducted in a semi-regenerativemanner, that is, a plurality of reforming zones are established inparallel flow, with interzone rehcaters to restore the desirable inlettemperatures, and a spare or swing reactor is manifolded into the pipingto permit any one of the process reactors to be taken off-stream,replaced by the swing reactor, and regenerated by exposure to acontrolled oxygen-containing atmosphere under combustion conditions toremove a coke-like material which deposits on the catalyst pellets as anunavoidable byproduct of the reforming reaction.

After reforming, the mixture of reformed hydrocarbons andrecycle-hydrogen-containing gas is ordinarily cooled to separateliquefiable hydrocarbons as a gross liquid product from thehydrogen-containing gas for recycle. This liquid product contains amixture of volatile hydrocarbon light ends, hydrocarbons in the gasolineboiling range, i.e. about initial boiling point to about 350420 F. finalboiling point in the ASTM distillation, as Well as a higher boilingmaterial. This higher boiling material, the amount and composition ofwhich depending upon the naphtha charging stock distillation range andthe severity of reforming, is or contains the catalytic reformatebottoms fraction or fractions which are subsequently oxidized inaccordance with the present invention. This bottoms fraction isvariously termed polyrner, post-gasoline, rerun bottoms, reformate bottsor bottoms, etc., and is composed almost entirely (98100%) of aromaticcompounds, predominantly condensed ring aromatics. It is not presentlyknown, nor is it important, precisely how this high boiling materialoriginates in the reforming process, but during reforming of a 200-400F. boiling range naphtha to a severity of, say, 95l05 research octanenumber clear, this fraction constitutes about 15 weight percent of thecharge naphtha.

The reformate bottoms fraction may be separated from gasoline boilingrange hydrocarbons (either before or after stabilization of suchhydrocarbons to remove light ends) by conventional fractionaldistillation in multi-tray distilling or rerun towers. The operation ofthese towers may be controlled to provide any desirable endpoint in thegasoline boiling range hydrocarbons which are taken overhead. Forexample, premium gasolines usually require that components blended intothem all have ASTM distillation endpoints of no higher than about 400 F.or even lower, although this may be exceeded by as much as 25 or so inparticular cases.

The reformate bottoms as it is taken from the rerun tower containshydrocarbons which boil within the range suitable for providing theoxidation feedstock herein, and may contain the higher boilinghydrocarbons which act as potent oxidation inhibitors. These inhibitors,if present, must be excluded from the oxidation feedstock, and suchexclusion may be conveniently accomplished by distillation in eitherbatch or continuous distillation apparatus. According to the preferredembodiment, the reformate bottoms fraction is distilled continuously ina plurality of fractional distilling columns to separate, in serialorder, (a) an extremely high boiling bottoms fraction, (b) a relativelylow boiling overhead fraction, and (c) a heart out of roughly 60-90volume percent of the reformate bottoms. This heart out may yet containsubstantial amounts of high boiling oxidation inhibitors, although theheart out itself may have a relatively narrow boiling range, e.g.458-575 F. at atmospheric pressure. The heart out is then, according tothe preferred embodiment, subjected to one or more additionaldistillation operations to isolate one or more fractions rich in aparticular alkyl naphthalene. Either an individual fraction thusobtained, a blend of two or more such fractions, or other combination offractions predominating in one or more alkyl naphthalenes may then beselected for a particular omdation.

It has been experimentally found that the heart cut described above maybe separated by fractional distillation into a number of individualcuts, each predominating in a single alkyl naphthalene, if thefractionation is carefully conducted in one or more distillation towerscontaining a comparatively large number of fractionating trays, e.g.30-200 trays, particularly if the distillation is conducted batchwise.Continuous distillation may of course be employed in largeinstallations. Distillation may be carried out at any suitable pressure,e.g. mm. mercury absolute to 100 p.s.i.g. or higher, although pressuresbelow atmospheric are conducive to finer separations. At a pressure of,say, 200 mm. mercury absolute a fraction boiling Within the range ofabout 360-365 F. (true boiling point methods), and representing about 10volume percent of a typical reformate bottoms, is found to be rich in2-methyl naphthalene. This may be oxidized in excellent yields tobeta-naphthoic acid. The fraction boiling at about 365-370 F. at 200 mm.mercury contains a predominance of l-methyl naphthalene, and may beoxidized to alpha-naphthoic acid. This 365-370 fraction represents about'volume percent of the total catalytic reformate bottoms. The fractionboiling at about 380395 F., constituting about eight percent ofreformate A bottoms, is enriched in 2-methyl naphthalene and may beoxidized, either alone or in combination with the firstmentionedfraction, to beta-naphthoic acid. The fraction boiling at about 395 F.,give or take about 3 F., at 200 mm. Hg is about eight percent of atypical reformate bottoms and predominates in 2,7-dimethyl naphthalene,which may be oxidized to naphthalene 2,7-dicarboxylic acid. The lastuseable fraction boils at about 400 (plus or minus about 3 F.), containsthe 1,6-dimethyl naphthalene and is about eight percent of the reformatebot toms; it may be oxidized to naphthalene 1,6-dicarboxylic acid.

It will be understood that the reformate bottoms fractions may beoxidized either individually or in any admixture, and need not beresolved into individual closeboiling fractions. It is furtherunderstood that the boiling ranges or points set forth above ofnecessity are dependent on the pressure at which said ranges or pointsare determined. The specific pressure of 200 mm. Hg absolute has beenused above for reasons of convenience and uniformity, but it isrecognized by the art that the boiling point of a hydrocarbon increaseswith an increase in pressure and decreases with a decrease. Hence thedesignated distillation pressure is to be considered only as adefinition of the boiling points of the respective fractions.

Components boiling above about 405 F. at 200 mm. mercury pressurecontain the unidentified oxidation inhibitor, and hence reformatebottoms fractions which are not substantially free from, i.e. containless than about 3-5 by weight, of such high boiling components cannot beoxidized in accordance with the present invention. Although the chemicalnature of this inhibitor material is unknown, as little as 13 percent inan otherwise-oxidizable reformate bottoms fraction leads, instead ofyields on the order of 50 mol percent or higher of naphthalenedicarboxylic acid, to only a few percent yield of dicarboxylic acid anda large amount of amorphous acidic or non-acidic material which cannotbe resolved into individual components. This inhibition is set forth inTests 1 and 2 described in a subsequent portion of this specification.

In the practice of the invention, the oxidation of alkylsubstitutednaphthalenes to the corresponding naphthalene carboxylic acids may beeffected by reacting such compounds with molecular oxygen, for example,air, in the conjoint presence of catalytic amounts of bromine and aheavy metal oxidation catalyst.

Metals of the group of heavy metals shown in the Periodic Chart ofElements, appearing on pages 56 and 57 of the Handbook of Chemistry, 8thedition, published by Handbook Publishers, Inc., Sandusky, Ohio (1952),have been found desirably applicable to this invention for furnishingthe metal or metal ion portion of the metalbromine catalyst. Of theheavy metal group, those metals having an atomic number not greater than84 have been found most suitable. Excellent results are obtained by theutilization of a metal having an atomic number from 23 to 28 inclusive.Particularly excellent results are obtained with one or more metals ofthe group consisting of manganese, cobalt, nickel, iron, chromium,vanadium, molybdenum, tungsten, tin and cerium. It has also been foundthat the catalytic amount of the metal may be either as a single metalor a combination of such metals. The metal may be added in elementalform, as the oxide or hydroxide, or in the form of a metal salt. Forexample, the metal manganese may be employed as the manganese salt of analiphatic carboxylic acid such as manganese acetate, manganese oleateand the like, as the manganese salt of an aromatic or cycloaliphaticcarboxylic acid, for example, manganese naphthenate, manganese toluate,etc., in the form of an organic complex, such as the acetylacetonate,the S-hydroxy-quinolate and the ethylene diarnine tetra-acetate, as Wellas manganese salts such as the borates, halides and nitrates which areare also efficacious.

The bromine may be added in elemental, combined or ionic form. As asource of available bromine, ammonium bromide or other compounds solublein the reaction medium may be employed. Satisfactory results have beenobtained for example, with potassium bromate. Tetrabromoethane, benzylbromide and the like may be employed if desired.

The amount of the metal catalyst employed is not critical and may be inthe range of from about .01 to about by weight or more based on thearomatic reactant charged. Such catalyst may comprise a single heavymetal or a mixture of two or more heavy metal oxidation catalysts. Wherethe heavy metal is introduced as a bromide salt, for example, asmanganese bromide, the proportions of manganese and bromine will be intheir stoichiometric proportions. The ratio of metal to bromine may bevaried, for example, within the range from about 1 to 10 atoms of heavymetal oxidation catalyst per atom of bromine to about 1 to 10 atoms ofbromine per atom of heavy metal.

The relation of temperature and pressure should be so regulated as toprovide liquid phase in the reaction Zone. Generally, the pressure mayhe in the range of atmospheric up to about 1500 p.s.i.g. The liquidphase may comprise all or a portion of the organic reactant or it maycomprise a reaction medium in which the organic reactant is dissolved orsuspended.

While a solvent need not be employed, in a preferred embodiment of theinvention the oxidation is conducted in the presence of a solvent mediumcomprising a monocarboxylic acid having from 2 to 8 carbon atoms in themolecule. Such acids which are free of hydrogen atoms attached totertiary carbon atoms are particularly advantageous as solvent sincethey have been found to be relatively stable or inert to oxidation inthe reaction system. Lower saturated aliphatic monocarboxylic acidshaving from 2 to 4 carbon atoms in the molecule are particularlyelfective solvents.

The preferred solvent is acetic acid usually employed in its glacialform. Although acetic acid is preferred, carboxylic acids such aspropionic acid, butyric acid, caproic acid, benzoic acid and the likemay be employed. Mixtures of these acids may be used. Where all theadvantages of an acid medium are not required, other inert media may beused.

Those skilled in the art will appreciate that the amount of solventemployed will be varied over wide limits. The amount of solvent utilizedis not critical but typically will be in the range of from about 0.1 toabout 10, desirably 0.5 to 4 times the weight of oxidizable startingmaterial.

As to the molecular ox gen-containing gas, there may be employedsubstantially 100% oxygen gas or gaseous mixtures containing lowerconcentrations of oxygen, for example, air. Such mixtures preferablyhave oxygen contents within the range of about 5% by volume to about 20%or more by volume. As such mixtures there may be employed air or airwhich has been diluted with gases such as nitrogen, CO and the like, orcorresponding mixtures prepared from substantially pure gaseous oxygenand such inert diluents may he used. The ratio of total oxygen fed intothe reaction mixture can be in the range of from about 0.5 to 50 molesor more of oxygen per mol of aromatic material.

The reaction temperature should be sufficiently high so that the desiredoxidation reaction occurs and yet not so high as to cause undesirablecharring or formation of tars. Thus temperatures in the range of 50-275C. desirably from l50250 C., may be employed.

By way of illustration, a virgin naphtha charging stock is catalyticallyreformed in the presence of a platinumalumina catalyst (or othercatalyst having dehydrocyclization activity) and the reformate productis fractionated to a gasoline boiling range material and a reformatebottoms. This bottoms is re-distilled to obtain a heart cut, which isthen carefully fractionated to produce cuts or fractions suitable forthe oxidation described herein.

The charge is a mixture of virgin naphtha derived from Gulf Coast, EastTexas, and West Texas sweet crude oils. Before charging to the reformer,it is desulfurized over a cobalt-molybdate type catalyst, and thenfractionated to exclude as a bottoms all hydrocarbons boiling aboveabout 400 F. in the ASTM distillation. Inspections of the naphtha, thedesulfurized naphtha, and tie fractionator overhead (reformer charge)are shown in Table 1 below.

The fractionator overhead constitutes the charge to a commercialcatalytic reforming unit employing about 0.1-1.0% platinum on aluminacatalyst disposed as pellets in live fixed-bed reactors and onefixed-bed swing reactor. Reactor inlet temperatures are about 900-970F., while the average reactor pressure is about 200-250 p.s.i.g. Arecycle gas ratio of about 3,0006,000 standard cubic feet ofhydrogen-containing gas per 42-gallon of charge is employed and thespace velocity units of weight of oil per weight of catalyst, is about14. In the reforming operation, naphtha taken as fractionator overheadis vaporized in a preheat furnace, combinated with hot recycle gas, andcharged to the lead reactor. After passing through the lead reactor, theetlluent is reheated in an. interstage furnace in order to return theprocess vapors to the desired reaction temperature before charging tothe next reactor. This reheating is repeated after the second, third andfourth reactors. The process vapors leaving the reactors are cooled in aseries of heat exchangers comprising the reboilers and preheaters forthe various towers in the fractionation sections of the plant, and arethen cooled further and charged to high-pressure separator. A portion ofthe hydrogen-rich separator gas is compressed, heated and returned tothe reactors as a recycle gas while net separator gas production ischarged to an absorption system for recovery of propane, butanes, andpentanes. The high pressure separator liquid is sent to a debutanizerfor removal of butanes and lighter components.

Because the dehydrocyclization reaction forms substantial amounts ofreformer bottoms having higher boiling points than are usable in motorgasolines, the debutanized reformate may be treated for removal of thesebottoms by rerunning in a distillation column, taking the gasolineboiling range material as an overhead reformed gasoline product andwithdrawing the reformate bottoms fraction for subsequent redistillationand use in accordance with the present invention. Typical product yieldsfrom. a reforming operation conducted to provide an ASTM product octanenumber, research method, without TEL addition, of are shown in Table 2below.

Inspections of debutanized gasoline and polymer or reformate bottomsobtained in this operation are shown in Table 3 below.

TABLE 3.-DEBUTANIZED GASOLINE AND RE- FORMATE BOTTOMS Gasoline BottomsASIM octane number:

D 908, research method, without TEL addition 100. 1 D 357, motor method,without TEL addition 87. 9 Gravity, deg. API 43. 5 9 5 Reid vaporpressure, p.s.i. 7.0 ASTM distillation, degrees Fahre Initial boilingpoint 106 460 IO-pereent point 180 480 30-percent point 248 500 50pereent point 284 508 70-pereent poi.nt 314 523 QO-percent point 346 588Final boiling point 408 700+ Hydrocarbon type, percent by volumeParqffins 22 Olefins Nsmhthenes Aromatics 75 99 The reformate bottomsfraction or polymer was continuously distilled in two towers, the firstof which separated about 17 volume percent bottoms as an aromaticsrichvery high boiling material, with as ASTM boiling range at atmosphericpressure of about 500670 F. The overhead was redistilled to excludeabout 3% as lights, leaving about 80 volume percent of the totalrefonnate bottoms as usable heart cut. This heart out was transferrcd toa laboratory-scale batch distillation column packed with IOU-mesh MrMcMahon packing and having an estimated 100 theoretical plates. Oncedistillation was under Way, the column was operated at a top pressure of200 mm. mercury absolute, and the column top temperatures were recordedas cut points. About 130 individual cuts were taken, each about 0.6volume percent of the total heart out charge. The cuts were maintainedin individual sample bottles, and were blended as needed. A plot showingvolume percent overhead versus column top temperature shows definiteplateaus corresponding to individual cuts or fractions which may beoxidized to produce the desired naphthalene carboxylic acids. In thisexample, the 360-365 P. fraction represented about 10 volume percent oftotal bottoms, the 365370 F. fraction was about 20%, the 380395 P.fraction about 8%, the 395 F. fraction about 12%, and the 401 P.fraction also about 12%.

Certain of the individual 0.6% cuts were oxidized in accordance with theinvention described herein and these oxidations are described below innumbered examples. The tests are demonstrations of the inhibitinge'fitect of materials boiling above about 405 F. at 200 millimetersmercury pressure.

Example 1 In this example, a reformate bottoms fraction having a boilingpoint of about 363 F. (about 360-365 F.) at 200 mm. was oxidized toobtain beta-naphthoic acid.

The sample oxidized had a boiling point of about 363 F. at 200 mm. Hgabsolute pressure, an API gravity of 9.9, and a refractive index of1.6046 at 20 C.; it represented 06 volume percent of the heart out. Amixture of 25 grams of the above-identified fraction, grams of glacialacetic acid, 1.2 grams of a mixture of cobalt acetate tetrahydrate andmanganese acetate tetrahydrate, together with 0.5 gram ammonium bromidein 6 ml. water, was introduced into a corrosion-resistant reactionvessel. Air was passed into the vessel at 400 F. and 400 p.s.i.g. at arate of 0.13 standard cubic foot per minute; When oxygen in theoil-gases reached 20.8 volume percent (condensable-free basis after 5.0cubic feet of air had been introduced) oxidation was terminated and thecontents of the reactor were removed. The acidic solvent was removed byevaporation and the residue dissolved in dilute sodium hydroxidesolution, filtered, and the filtrate acidified with hydrochloric acid.The precipitated solid was filtered and after drying weighed 24.0 grams.It was shown to be beta-naphthoic acid by melting point (found 179183C., literature 185 C.), neutral equivalent (found 173, theory 172)and'infra-red spectrum.

1 Example 2 In this example, a reformate bottoms fraction boiling in therange of about 365370 F. was oxidized in the liquid phase to obtainalpha-naphthoic acid.

The sample oxidized had a boiling point at 200 mm. Hg absolute of about369 R, an API gravity of 7.2, and a refractive index at 20 C. of 1.6158.It represented 0.6 volume percent of the heart out. A mixture of 25grams of this fraction, 150 grams of glacial acetic acid, 1.2 grams ofmixed cobalt acetate tetrahydrate and manganese acetate tetrahydrate,and 0.5 gram ammonium bromide in 6 ml. water was oxidized with air at400 p.s.i.g. at a rate of 0.13 cubic foot per minute. After theintroduction of 5.5 standard cubic feet of air, oxygen in the elf-gasrose to 20.8% and the reaction was terminated. The reactor contents werecooled and removed. The acetic acid solvent was removed by evaporationon a steam bath, and the residue dissolved in dilute sodium hdyroxidesolution, filtered, and acidified with hydrochloric acid to precipitatea solid acid. After drying, the solid acid weighed 25.0 grams and wasshown to be alpha-naphthoic acid by the melting point (found 150- C.,literature C.), neutral equivalent (found 174, theory 174) and infra-redspectrum.

Example 3 In this example, a reformer bottoms fraction having a boilingrange of about 380-395 F. at 200 mm. Hg absolute pressure was oxidizedin the liquid phase to prepare beta-naphthoic acid.

The sample oxidized had a boiling point of about 391 F. at 200 mm., anAPI gravity of 11.0, and a refractive index at 20 C. of 1.5988; it was0.6 volume percent of the heart out. A mixture of 25 grams of thisfraction, 150 grams glacial acetic acid, 1.2 grams of mixed cobaltacetate tetrahydrate and manganese acetate tetrahydrate, and 0.5 gramammonium bromide in 6 ml. water was reacted with air at 400 F. and 400p.s.i.g. Air was intro duced at a rate of 0.13 cubic foot per minute,and when, after 8.5 standard cubic feet of air had been admitted,

oxygen in the oli-gas returned to 20.8%, the reaction was terminated.The reactor contents were cooled and removed, after which the aceticacid was removed by evaporation on the steam bath. The residue wasdissolved in dilute sodium hydroxide solution, filtered, and thefiltrate acidified with hydrochloric acid. The precipitated solid wascollected on a filter. After drying, the solid acid weighed 21 grams.

This solid material was worked up by redissolving it in sodium hydroxidesolution, treating the solution with adsorbent charcoal, and filteringand acidifying with hydrochloric acid to precipitate the solid acids.The solid acids were then worked up by fractional crystallization fromethanol. The solid acid was found to contain 15 grams of beta naphthoicacid and 6 grams of unidentified dibasic acids. The beta naphthoic acidwas identified by melting point, neutral equivalent (found 171, theory172), and comparison of the infra-red spectrum with the spectrum ofauthentic beta naphthoic acid.

Example 4 In this example, a reformer bottoms fraction having a boilingrange of around 395 F. at 200 mm. Hg was oxidized in the liquid phase toyield naphthalene-2,7-dicarboxylic acid.

The sample oxidized had a boiling point of about 396 F. at 200 mm. Hg,an API gravity of 11.2, and a refractive index of 1.6051. This fractionrepresented 1.2 volume percent of the heart cut. A mixture of 25 gramsof the reformate bottoms fraction, 150 grams glacial acetic acid, 1.2grams of mixed cobalt acetate tetrahydrate and manganese acetatetetrahydrate, and 0.5 gram ammonium bromide in 6 ml. water was heated ina reactor at 400 F. while air at 400 p.s.i.g. was passed into thereactor at the rate of 0.13 cubic foot per minute. After 6.5 standardcubic feet of air had been used, the reaction was terminated and thereactor contents were then allowed .to cool and were subsequentlywithdrawn. The acetic acid solvent was removed by evaporation on thesteam bath, and the residue dissolved in dilute sodium hydroxidesolution, filtered, the filtrate acidified with hydrochloric acid, andthe precipitated solid cooled on a filter. After drying, the solid acidweighed 21 grams and had a neutral equivalent of 116. Theory fornaphthalene dicarboxylic acids is 108. This product was dissolved in 450cc. hot ethanol, and on cooling yielded a precipitate amounting to10-15% by weight of the total product. This precipitated material wasshown to be naphthalene 2,7-dicarboxylic acid by comparing its infraredspectrum with the spectrum of authentic 2,7dicarboxylic acid.

Example 5 In this example, a reformate bottoms fraction boiling around400 F. at 200 mm. Hg was oxidized to preparenaphthalene-1,6-dicarboxylic acid.

This sample had a boiling point of 401 F. at 200 mm. Hg, an API gravityof 9.7, a refractive index of 1.6082 at 20 C., and represented 0.6volume percent of the heart cut. A mixture of 25 grams of bottomsfraction, 150 grams acetic acid, 1.2 grams cobalt and manganese acetatetetrahydrates, and 0.5 gram ammonium bromide in 6 ml. water was heatedin a reactor at 400 F. while air at 400 p.s.i.g. was passed through thereaction mixture at a rate of 0.13 standard cubic foot per minute. When8.0 cubic feet of air had been introduced, oxygen in the off-gasreturned to 20.8% and the reaction was terminated. The reactor contentswere removed and cooled, the acetic acid solvent was removed byevaporation on a steam bath, and the residue dissolved in dilute sodiumhydroxide solution, filtered, and the filtrate acidified withhydrochloric acid to precipitate a solid acid product. This solid acidweighed 32 grams (80 weight percent yield) and had a neutral equivalentof 116 (theory for a naphthaiene dicarboxylic acid is 108). Theinfra-red spectrum of this acid was essentially identical to thespectrum of authentic naphthalene 1,6-dicarboxylic acid. The infraredspectrum was not changed after treatment with charcoal andcrystallization from ethanol. The infra-red spectrum of the dimethylester of this product was also essentially identical with the spectrumof a dimethyl ester of authentic naphthalene 1,6-dicarboxylic acid.

TEST 1 In this test, a reformate bottoms fraction composed ofhydrocarbons boiling above 405 F. was oxidized in the liquid phase, andgave a black, syrupy mass which could not be worked up.

The cut oxidized had a boiling point of 408 F. at 200 mm. Hg, an APIgravity of 9.6, and a refractive index of 1.6129 at 20 C. It represented0.6 volume percent of the heart cut. A mixture of 25 grams of this highboiling material, grams glacial acetic acid, 1.2 grams mixed cobalt andmanganese acetate tetrahydrates, and 0.5 gram ammonium bromide in 6 ml.water was heated at 400 F. while air at 400 p.s.i.g. was passed throughthe mixture at the rate of 0.13 cubic foot per minute. After completionof the reaction, the acetic acid solvent was removed by evaporation on asteam bath to yield a black, syrupy mass which could not be worked up orseparated by conventional means into pure components. By chromatographicanalysis, it was found that this syrupy mass contained about 9.0 gramsof methyl naphthoic acids and 8.0 grams of one or more naphthalenedicarboxylic acids, plus unidentified neutral resinous products.

In a modification of the above test, a second portion of the 408 F.boiling range reformate bottoms cut was re peatedly crystallized fromethanol to furnish about 60 Weight percent of substantially pure2,3-dimethyl naphthalene (by infra-red analysis). This was oxidizedunder conditions duplicating those of the test and yielded 2,3-dicarboxylic acid in 63 mole percent yield. Thus it is evident that aminor quantity of some material in bottoms fraction boiling above 405 F.exerts a powerful inhibition on the oxidation reaction.

TEST 2 To further demonstrate the inhibiting action of materials boilingabove 405 F. at 200 mm. Hg, an additional test was conducted using amixture of 10 grams of the fraction successfully oxidized in Example 4,10 grams of the fraction successfully oxidized in Example 5, and 10grams of the reformate bottoms fraction boiling at 408 F. and whichwould not oxidize in Test 1. Recalling that the reformate bottomsfraction in Test 1 contained only 40% of unidentified inhibitingmaterial, the blend of fractions herein employed contained at most only13.3% inhibitor.

A mixture of 30 grams of the above described blended fraction, 150 gramsacetic acid, 1.2 grams mixed cobalt and manganese acetate tetrahydrates,and 0.5 gram ammonium bromide in 6 ml. water was heated at 400 F. Whileair at 400 p.s.i.g. was passed through the mixture at a rate of 0.13cubic foot per minute. When oxygen in the oft-gas returned to 20.8%, thereactor contents were cooled and removed. The acetic acid solvent wasremoved by evaporation on the steam bath. Work-up gave 7.0 grams ofunreacted hydrocarbon, 7.0 grams of nonacidic black tar, and 22.0 grantsof black acidic syrup which could not be resolved into crystallizableacid products.

From the foregoing presentation it is apparent then that the inventiveprocess provides an outstanding method for preparing naphthalenecarboxylic acids. The charging stock is readily available, and willbecome even more obtainable as automobile octane number requirementsdemand increased catalytic reforming severity. Thus the outstandingplasticizers, pesticides, resins, and polyester fibers which are basedon naphthalene carboxylic acids and which heretofore had been of limitedcommercial utility by reason of their unavailability may now becomeimportant products of commerce.

We claim:

1. In a process for the preparation or" a naphthalene carboxylic acidwherein a catalytic reformate bottoms fraction is reacted with molecularoxygen-containing gas in the liquid phase and in the presence of acatalyst comprising in conjoint presence bromine and a heavy metaloxidation catalyst, the improvement of the step, prior to such reaction,of separating from said catalytic reformate bottoms fraction thosehydrocarbons having a true boiling point at 200 mm. Hg absolute pressureof above 405 F. whereby inhibition of the oxidation reaction is avoided.

2. Process of claim 1 wherein said catalytic reformate bottoms fractionhas a true boiling range at 200 mm. Hg absolute pressure of about 360365F., and the naphtha- 1 1 lene carboxylic acid thus prepared isbeta-naphthoic acid.

3. Process of claim 1 wherein said catalytic reformate bottoms fractionhas a true boiling range at 200 mm. Hg absolute of about 365-370 F., andthe naphthalene carboxylic acid thus prepared is alpha-naphthoic acid.

4. Process of claim 1 wherein said catalytic reformate bottoms fractionhas a true boiling range at 200 mm. Hg absolute pressure of about380-395 F. and the naphthalene carboxylic acid thus prepared isbeta-naphthoic acid.

5. Process of claim 1 wherein said catalytic reformate bottoms fractionis a mixture of two such fractions having true boiling ranges at 200 mm.Hg absolute pressure of about 360-365 F. and about 380-695 F, and thenaphthalene carboXylic acid thus prepared is beta-naphthoic acid.

6. Process of claim 1 wherein said catalytic reformate bottoms fractionhas a true boiling range at 200 mm. Hg absolute pressure of about 395F., and the naphthalene carboxylic acid thus prepared isnaphthalene-2,7-dicarboxylic acid.

7. Process of claim 1 wherein said catalytic reformate bottoms fractionhas a true boiling range at 200 mm. Hg absolute pressure of about 401F., and the naphthalene carboxylic acid thus prepared isnaphthalene-1,6-dicarboxylic acid.

8. Process of claim 1 wherein said heavy metal oxida tion catalyst hasan atomic number of 23 to 28, inclusive.

9. Process of claim 1 wherein said heavy metal is selected from thegroup consisting of manganese, cobalt, and mixtures thereof. 7 i 7References Cited in the file of this patent UNITED STATES PATENTS VSmith Aug. 17, 1954'

1. IN A PROCESS FOR THE PREPARATION OF A NAPHTHALENE CARBOXYLIC ACIDWHEREIN A CATALYTIC REFORMATE BOTTOMS FRACTION IS REACTED WITH MOLECULAROXYGEN-CONTAINING GAS IN THE LIQUID PHASE AND IN THE PRESENCE OF ACATALYST COMPRISING IN CONJOINT PRESENCE BROMINE AND A HEAVY METALOXIDATION CATALYST, THE IMPROVEMENT OF THE STEP, PRIOR TO SUCH REACTION,OF SEPARATING FROM SAID CATALYTIC REFORMATE BOTTOMS FRACTION THOSEHYDROCARBONS HAVING A TRUE BOILING POINT AT 200 MM. HG ABSOLUTE PRESSUREOF ABOVE 405*F. WHEREBY INHIBITION OF THE OXIDATION REACTION IS AVOIDED.